Essential plant nutrients can be divided into two groups, the macronutrients, both primary and secondary, and micronutrients. Plants access primary nutrients including nitrogen, phosphorus, and potassium from the soil and hence they make up the major part of fertilizers used to supplement soils that are lacking in these nutrients.
According to the conventional fertilizer standards, the chemical makeup or analysis of fertilizers is expressed in percentages (by weight) of the essential primary nutrients nitrogen, phosphorus, and potassium. More specifically, when expressing the fertilizer formula, the first value represents the percent of nitrogen expressed on the elemental basis as “total nitrogen” (N), the second value represents the percent of phosphorus expressed on the oxide basis as “available phosphoric acid” (P2O5), and the third value represents the percent of potassium also expressed on the oxide basis as “available potassium oxide” (K2O), or otherwise known as the expression (N—P2O5—K2O).
Even though the phosphorus and potassium amounts are expressed in their oxide forms, there technically is no P2O5 or K2O in fertilizers. Phosphorus exists most commonly as monocalcium phosphate, but also occurs as other calcium or ammonium phosphates. Potassium is ordinarily in the form of potassium chloride or sulfate. Conversions from the oxide forms of P and K to the elemental expression (N—P—K) can be made using the following formulas:% P=% P2O5×0.437% K=% K2O×0.826% P2O5=% P×2.29% K2O=% K×1.21
In addition to the primary nutrients that are made available to plants via fertilizer added to soil, secondary nutrients and micronutrients are also essential for plant growth. These are required in much smaller amounts than those of the primary nutrients. Secondary nutrients include sulfur (S), calcium (Ca), and magnesium (Mg). Micronutrients include, but are not limited to, for example, boron (B), zinc (Zn), manganese (Mn), nickel (Ni), molybdenum (Mo), copper (Cu), iron (Fe), and chlorine (Cl).
Among the micronutrients, boron deficiency is a major concern in many agricultural areas particularly in sandy soils. Fertilization with boron presents a challenge due to the narrow window between nutrient deficiency and toxicity. The amount of boron available to a plant's root zone should be carefully considered as plants are highly sensitive to boron and need only very small amounts. The presence of high levels of boron can pose risks of seedling injury from boron toxicity. Traditional methods of bulk blending boron with fertilizer granules, such as borax, are ineffective or unsuitable due to uneven boron distribution, which can result in too high levels of B close to the granule and deficient levels further away.
To aid in even distribution of boron, the applicant of the present application proposes that different sources of boron added to muriate of potash (MOP) granules before or during compaction, as described in U.S. Pat. No. 9,266,784, reduces the occurrence of boron toxicity and provides an even application of small amounts of boron required by the plant.
Another challenge with respect to boron fertilizer management is providing sufficient boron during all plant growth stages, as this micronutrient plays crucial roles from seedling to flowering. Commonly used sources of soluble boron, such as sodium tetraborate, are highly water soluble and therefore tend to have extremely high mobility in soils compared to most other nutrients, which the exception of nitrate and sulfate, as it is predominately uncharged in most soils. Soluble boron sources can therefore be easily leached from soils before being taken up by the roots, particularly in rainy environments, resulting in boron deficiency later in the growing season, particularly at flowering. It is therefore a difficult balance of providing an appropriate level of boron to ensure the plant is getting the essential nutrient during the growing season while minimizing the occurrence of boron toxicity.
There remains a need for a boron fertilizer product with both fast and slow release characteristics to ensure even and sufficient distribution of boron to the root zone of plants, while reducing the risk of boron toxicity.